Flexible couplings are used to transmit rotational forces between two non-collinear shafts, the rotational axis of which intersect approximately in the center of the coupling. "Rotational axis" refers to the axis about which the shaft rotates. The non-collinear orientation of the coupled shafts described above is referred to as "angular misalignment".
Typical flexible coupling assemblies embody attachment means for attaching the coupling to the driving and driven shafts respectively. At least one load transmitting element is used to transmit forces between the respective attachment means despite angular misalignment of the two shafts.
Prior flexible couplings have used either rigid or resilient load transmitting elements. Typical rigid load transmitting elements comprise a rod or rocker having bearing surfaces at both ends which permit the element to rock or pivot, relative to the attachment means, in response to angular misalignment of the driving and driven shafts. A disadvantage with this type of load transmitting element is that it will develop free play and, unless the motion along the axis ("axial motion") of the respective attachment means is constrained, torque applied to this type of coupling will cause it to disassemble.
In order to provide a constraint against the tendency to disassemble and development of free play inherent in couplings having rigid load transferring elements, couplings have been developed which utilize a resilient material between conforming surfaces of the attachment means as transmitting elements. A disadvantage with resilient load transmitting elements is that if they are to be large enough to withstand large torque loads, excessive resistance to angular misalignment arises due to the forces required to deform the resilient elements to flex the coupling.
While attempts have been made to reinforce a resilient load transferring element by using two layers of resilient material separated by a rigid material, the decrease in thickness of the resilient portion of such an element greatly reduces the angular misalignment which a coupling embodying such an element can accommodate.